1. Field of the Invention
This invention relates to X-ray exposure equipment, and more particularly to X-ray exposure equipment which makes use of, for example, synchrotron radiation.
2. Description of the Prior Art
Synchrotron radiation radiated from a storage ring serves as a source of X-rays which radiates in a fan-shaped-beam having a broad band spectrum, the wavelength of which ranges from hard X-rays to visible light. Such a beam has a large divergence angle in a horizontal direction but has a small divergence angle in a vertical direction. X-ray exposure equipment which makes use of such synchrotron radiation as a source of X-rays is already known and disclosed, for example, in Nuclear Instruments and Methods in Physics Research, A246, 1986, pp. 658-667. The X-ray exposure equipment is shown in FIG. 6.
Referring to FIG. 6, the X-ray exposure equipment consists of an X-ray source 1 in the form of a point light source for radiating therefrom X-rays having divergence angles in the horizontal and vertical directions, a vacuum window 4 formed, for example, from a beryllium film, a lithographic plane 5, and a plane X-ray reflecting mirror 8.
In operation, the plane X-ray reflecting mirror 8 intercepts hard X-rays while the vacuum window 4 formed from a beryllium film or the like intercepts a long wavelength band longer than several tens of angstroms. The plane X-ray reflecting mirror 8 and the vacuum window 4 constitute an X-ray optical system. Thus, X-rays of a wavelength band around 10 angstroms which is appropriate for the X-ray lithography can be extracted from the X-ray optical system.
Conventional X-ray exposure equipment is constructed in a manner such as that described above. In conventional X-ray exposure equipment, an aperture of the X-ray optical system with respect to the point light source 1 depends upon the size of the vacuum window 4 located on the downstream side, and accordingly, it cannot have a large size. Consequently, only very small part of the synchrotron radiation which spreads to a great extent in a horizontal direction can be extracted to the lithographic plane 5. Particularly, when synchrotron radiation from a compact storage ring for semiconductor device production is utilized, the intensity of a synchrotron radiation is not high, and accordingly, there is a problem that a sufficiently high intensity of X-rays cannot be assured on the lithographic plane 5.
Further, synchrotron radiation is irradiated upon the lithographic plane 5 while maintaining the synchrotron radiation's divergence angle. Consequently, as the distance from the original point on the lithographic plane 5 which is defined as an interception point of the principal optical axis of the X-ray optical system and the lithographic plane 5 increases particularly in a horizontal direction, displacement of incidence of X-rays to the lithographic plane 5 from normal incidence increases progressively. Accordingly, there is another problem that displacement of a replicated pattern on the lithographic plane 5 from an X-ray mask pattern increases as the distance from the original point increases in a horizontal direction.